Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $65.82   12.658%   $74.1515   $74.15   $74.15   $74.20  
  Purchase #2 $125.45   7.343%   $134.6618   $134.66   $134.65   $134.70  
  Purchase #3 $34.69   9.509%   $37.9887   $37.99   $38.00   $38.00  
  Purchase #4 $19.42   4.616%   $20.3164   $20.32   $20.30   $20.30  
  Purchase #5 $158.75   12.388%   $178.416   $178.42   $178.40   $178.40  
  Purchase #6 $224.51   4.677%   $235.0103   $235.01   $235.00   $235.00  
  Purchase #7 $87.26   8.462%   $94.6439   $94.64   $94.65   $94.60  
  7 purchase totals = $715.90       $775.1886   $775.19   $775.15   $775.20